A peritoneal dialysis system comprising a housing, a stepper motor housed by the housing, a pump head in operable communication with the stepper motor, a disposable unit operable with the housing and an encoder operably coupled to the stepper motor. The disposable unit includes a membrane operable with the pump head and wherein the housing and the disposable unit are configured to allow a negative pressure to be applied to the pump head and the membrane. The stepper motor is configured to move the pump head towards and away from the disposable unit. The encoder is operable with a position detection apparatus located to detect a position of the pump head relative to a reference position.
